What Have I Found?

One of our fungi fanatics found these mushrooms last weekend near Garrick, Saskatchewan – please see message below and comment on the post if you have any ideas!

“(The mushrooms) look yellow in the photos, but I think they were white on Saturday, and on Sunday, after the rain started, they were a silvery/grey/brownish colour. I did not know to cut out the base of the mushroom for identification purposes, so I do not know what the base of the mushroom is like. The mushrooms were growing in crowded clusters, and the clusters stretched in a line for 20 or more feet, if my estimation is correct. The mushrooms were growing on the ground, not on wood. The forest surrounding the mushrooms includes aspen, spruce, and possibly a bit of black poplar. The area where the mushrooms were growing included mainly aspen. The spore print from the mushrooms is a cream/ivory colour (I mistakenly made the spore print on a piece of white paper, so maybe the print would look white if it was on a different colour of paper).”